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Air con woes

 
Old 07-06-2019, 02:42 PM
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vanster
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Default Air con woes

I'm sure this is a beat up subject but I'm stumped once again. My AC was blowing inconsistently super cold then cool and it went back and forth for the past 1000 miles or so. I figured it was low on R12. Last weekend coming back thru 100 degree heat it would not blow cold at all. Yesterday I topped off the system with a can of R12. Still doesn't blow cold or even cool. Tried to add a second can but it would only take about half. The window in the dryer shows clear, no bubbles and the system is not that old. (20k at best) At first the rear air felt like it was working but still warm out of the front. The WSM is useless to me on this one. I'm wondering if the control unit is defective.
Question is where to start looking first, keeping in mind that everything from the firewall forward is recent has been rebuilt. I'm sure there is a small leak in the system but with it topped off it should work. I last topped it off was little over a year ago or more.
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Old 07-06-2019, 02:46 PM
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My guess would be that the compressor clutch is slipping, have you checked the air gap and electrical resistance as per WSM?
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Old 07-06-2019, 03:09 PM
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Thanks, I'll check the compressor clutch.
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Old 07-06-2019, 03:29 PM
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it would also be a good idea to check the HVAC vacuum and test the pods,
remove the left console cover to get to the lines.
NOTE it would be better to see s a few bubbles in the window compared to not seeing any as you could have over filled the system.
Also check the expansion valve as the drier could have ruptured and thus dessicant is plugging the valve,
to do this remove the cowl cover then with the system running see if the small line is hot and fat line icy cold at the expansion valve
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Old 07-06-2019, 04:33 PM
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First thing to do is to see if the A/C compressor clutch is engaging at all. Easiest with two people: one with finger on the A/C push button the other one with a flash light looking at the nose of the compressor. During testing note if the light for the button is coming on when pressed.

Do that and report back.
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Old 07-06-2019, 07:31 PM
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Well....the small line and the fat line do not change in temp.
I can't see or hear the compressor go on. As I recall when the AC button is depressed you can hear the compressor turn on. The light is on when the button is depressed
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Old 07-06-2019, 07:36 PM
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Check to see if the wire that powers the clutch got cut by the smog pump belt.

It's a fairly common thing that happened to me and caused a similar issue.

It could also be that the wire just came unplugged slowly over time, which would cause the intermittent problem you're having.
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Old 07-06-2019, 07:45 PM
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Verify clutch operation, and check clutch voltage at the freeze switch terminals without disconnecting anything. If you have voltage and no clutch engage, you'd be looking at the charge level, then the 14-pin connector cleanliness.. Note that there are no sight-glass bubbles when the compressor isn't running. Back to the voltage... If there are low or no volts showing at the freeze switch, unplug the compressor lead near the dipstick tube above the clutch, and test again. If you now have voltage at the freeze switch, the control head relay is your target.
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Old 07-06-2019, 08:30 PM
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Should the outer part of the pully spin when the compressor is working?
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Old 07-06-2019, 08:44 PM
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Probably already done this but check the freeze switch...I had one burn out that was less than 5 years old. With car cold, hook up multimeter and make sure there is continuity at the wire connections. Don't need car / AC on or anything...just check that the freeze switch at room/avg temp is allowing continuity.
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Old 07-06-2019, 09:05 PM
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Originally Posted by vanster View Post
Should the outer part of the pully spin when the compressor is working?
The inside should be spinning. The clutch engages to allow the outer spinning pulley to power the inner one and drive the compressor.
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Old 07-06-2019, 09:48 PM
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Blake
The outer never spins, regardless on or off

Also, 928 noobie , where is the freeze switich?
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Old 07-06-2019, 10:08 PM
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Originally Posted by vanster View Post
Blake
The outer never spins, regardless on or off

Also, 928 noobie , where is the freeze switich?
If the outer doesn't spin then the belt is slipping... a lot. Is the crank bolt tight or the belt old?

I cannot really tell from the angle of the picture but is the belt even on it? It may have jumped off.

The freeze switch is located on the back of the HVAC box with a metal probe (capillary tube) going through the box into the evaporator. It has 2 spade connectors on it.
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Old 07-06-2019, 10:10 PM
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I think honing in on the clutch activation is a good place to start. The clutch is activated but the dash switch and then through a relay in the hvac head unit. The circuit is grounded through the compressor and engine chassis.

There are are several points of failure to test.
1. You can test the compressor clutch by applying 12v to the terminal (engine off) you should head the lick of the magnet engaging the clutch onto the drive pulley

2. You can test the activation of the circuit by attaching your multimeter (volts) to the lead into the compressor and a know ground point. With the ignition on you should see 0 volts with the ac switch In the off position and 12v in the on position.

Hope me this was helpful, if you need a freeze switch I have a known functioning, calibrated, tested unit you can have. But test yours first. Search for the test procedure.

FYI here is the factory publication for testing it’s a bit more useful than the wsm https://drive.google.com/file/d/1UVU...w?usp=drivesdk
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Old 07-06-2019, 10:51 PM
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AC goes through several tests before compressor is allowed to run:

1. Defrost: if setting is on de-ice, won't run
2. Now we go to freeze switch..simple test for continuity using multimeter
3. Pressure switch on drier


Can't remember may have missed one...?

Any of these things will prevent AC from running, this is assuming relays etc. are all in good shape.

If your climate control relay for the AC is working, get a relay from an auto parts store and put it in the engine compartment so your compressor draws from a better source..the wire is thin and runs over the engine so resistance increases.
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